Lowdown on PHP/MYSQL Based Pixel Scripts

Hi !

Can someone give me the lowdown on the various pixel scripts that are out there...what's the best, what's the cheapest, which will work well on php/mysql systems, etc... I'm currently looking at GPix (http://www.*****.com/millionpixelscript.php), and similar offerings from textmedia.de and milliondollarscript.com and a few others). I want something that is scalable, works with Paypal, is php-based, and not too expensive.
Need your suggestions.

Thanks in advance!